The invention relates to chemical flash lamps and particularly to flash lamps which are electrically activated.
As described, many of the flash lamps defined in the above co-pending applications employ at least one thin conductive coating, e.g. tin oxide, on the exterior surface of the lamp's envelope. Accordingly, when an electrical pulse is supplied to these coatings, such as through a resilient contact in engagement therewith, activation of the lamp is achieved. In those lamps utilizing a single lead within the envelope, firing is achieved by applying the needed activating potential across the lead and the external conductive coating. In leadless lamps, activation may be accomplished by developing the required potential across a pair of coatings spacedly oriented on the envelope's external surface.
Typical chemical flash lamps, including those described above, include a quantity of combustible material such as shredded zirconium or hafnium within the lamp's hermetically sealed glass envelope. A combustion-supporting gas such as oxygen is also provided within the envelope and established at a pressure well above one atmosphere. During lamp flashing, the glass envelope is subjected to severe thermal shock and, as a result, cracks and crazes occur within the glass. At high internal pressures, containment of the glass becomes practically impossible. In order to reinforce the glass and improve its containment capability it has been common practice to apply a protective, insulative layer or coating about the envelope's external surface. Several methods are utilized in the industry, including dipping, fluidized bed coating, spraying, and even vacuum-drawing a preformed polycarbonate sleeve about the envelope. Of the above, the preferred method is dipping wherein the envelope is dipped several times in a lacquer solution containing a solvent and a selected resin such as cellulose acetate. After each dip, the lamp is dried to permit evaporation of the solvent and leave the desired plastic resin coating.
The presence of an insulative plastic layer or polycarbonate sleeve over the conductive coatings in the aforementioned leadless and single lead lamps presents a problem, however, when providing the necessary electrical connection to the conductor. As described in the above co-pending applications, the method used requires removal of a portion of the coating in the region above the conductive coating where contact is desired. This method has disadvantages, however, in that additional manufacturing steps, e.g., masking, are required. Such a process is both time-consuming and expensive from a production standpoint. Even further, the absence of portions of the protective coatings may result in the described containment problems occurring within these regions.
It is believed, therefore, that an improved coupling path through an insulative layer on a flash lamp envelope for enhancing electrical connection between a conductive coating located under the layer and a contact located externally of the lamp would constitute an advancement in the art.